1. Field of the Invention
The present invention relates to methods for driving plasma display panels, and more particularly relates to the improvement of a driving method for resetting.
2. Description of the Related Art
FIG. 1 shows the structure of a plasma display panel (hereinafter referred to as a PDP).
The PDP is manufactured by attaching a front base plate 10 and a rear base plate 20 to each other. The front base plate 10 includes a plurality of pairs of display electrodes (X electrodes 11 and Y electrodes 12). A dielectric layer 13 covers these electrodes, and a protective film-14 made of MgO or the like covers the dielectric layer 13.
A plurality of address electrodes (A electrodes 21) is arranged on the rear base plate 20. A dielectric layer 23 covers the A electrodes 21. Barrier ribs 25 partitioning discharge spaces into regions are disposed between the adjacent A electrodes 21. Each of the regions is applied with one of red, green, and blue fluorescent materials 26R, 26G, and 26B.
The front base plate 10 and the rear base plate 20 are attached to each other so that the A electrodes 21 intersect the X electrodes 11 and the Y electrodes 12. One cell is arranged at the intersection of each of the A electrodes 21 and each pair of the X electrodes 11 and the Y electrodes 12. One pixel of the PDP is formed of three adjacent cells colored red, green, and blue.
Referring to FIG. 2, a method for driving the PDP to perform display will now be described. The PDP performs grayscale display by dividing one field into a plurality of sub-fields having different light emitting periods. FIG. 2 illustrates 28 gray-level control (that is, 256 gray levels (28=256)). One sub-field (hereinafter referred to as SF) consists of a resetting period, an addressing period, and a sustaining period (light-emitting period).
The light-emitting periods in the SFs are arranged to derive a ratio of 1:2:4:8:16:32:64:128 or a ratio close to this ratio. For example, the gray-level 10 is displayed by turning ON a cell in SF2 that has an weight of 2 and SF4 that has an weight of 8 and turning OFF the cell in the remaining SFs.
The operation of the PDP during one SF will now be described. As described above, one SF consists of the resetting period, addressing period, and sustaining period. In the resetting period, the charge states (wall charges) of all cells are set to a predetermined state. In the addressing period, a selective writing discharge or erasing discharge is initiated in each desired cell to be displayed. The charge state of each cell is changed by the selective writing discharge or erasing discharge. In the sustaining period, a sustaining discharge by a sustaining pulse is caused only in the cell whose charge state has been changed.
FIG. 3 shows voltage waveforms applied to the electrodes. In a period excluding the addressing period during which driving waveforms are selectively applied to an A electrode group and a Y electrode group, that is, in the resetting period and the sustaining period, the common waveforms are applied to the corresponding electrode groups. In contrast, in the addressing period, data pulses (also referred to as address pulses) A(1) to A(n) in accordance with display data are applied to the individual A electrodes 21, and scan pulses ScP1 to ScPn that are separated in the time domain to perform line selection are applied to the individual Y electrodes 12. In the resetting period, a gradually increasing voltage waveform (positive ramp wave) RPa and a gradually decreasing voltage waveform (negative ramp wave) RPb are applied to the Y electrodes 12.
FIG. 4 shows the basic resetting operation. A resetting waveform used here is a waveform combining the positive ramp wave and the negative ramp wave. In order to simply describe the principle, the resetting operation between two electrodes, that is, an α electrode and β electrode, will now be described. The α electrode and the β electrode described here refer to two electrodes of the X electrode, Y electrode, and A electrode. The phrase “voltage applied between the α and β electrodes (or α-β applied voltage)” refers to a voltage applied between the α electrode and the β electrode (difference (voltage) between the electrodes), and, more specifically, refers to a potential (relative value) of the α electrode on the basis of the β electrode (the same applies to the following description). One of the XY voltage waveform and the AY voltage waveform in the resetting period shown in FIG. 3 serving as α-β voltage waveform corresponds to the waveform shown in FIG. 4.
Referring to FIG. 4, first, a negative ramp wave having an amplitude of −VR1 (positive or negative is indicated by the sign of the amplitude) is applied between the α and β electrodes, which is followed by application of a positive ramp wave with an amplitude of VR2. The solid line represents the voltage applied between the electrodes. The dotted line, broken line, and dotted-chain line represent the sign-inverted voltages (wall voltages) representing the charge state of a cell. Resetting refers to setting the states of cells to the same state regardless of their previous states (turned-ON or turned-OFF states). Discussion of the resetting operation requires investigation of each cell's state at the time the previous SF has ended. A wall voltage of a cell that has been turned ON in the previous SF (referred to as a wall voltage of a “turned-ON cell”) is represented by the broken line. A wall voltage of a cell that has been turned OFF in the previous SF (referred to as a wall voltage of a “turned-OFF cell”) is represented by the dotted line.
Since a voltage component (wall voltage) due to the charging by the wall charge is added to an applied voltage component, the effective voltage required by each cell's discharge space (hereinafter refereed to as the “cell voltage”) is:
cell voltage=applied voltage+wall voltage.
Since the sign of the wall voltage is inverted, the cell voltage in FIG. 4 corresponds to the length between the dotted line (or the broken line or the dotted-chain line) and the solid line (the same applies to the following description). The cell voltage is positive when the solid line is above the dotted line (or the broken line or the dotted-chain line), whereas the cell voltage is negative when the solid line is below the dotted line (or the broken line or the dotted-chain line). For example, in FIG. 4, the cell voltage upon application of the negative ramp wave in the first half is negative, whereas the cell voltage upon application of the positive ramp wave in the second half is positive.
Prior to the start of resetting (time to), the wall voltages of both the turned-ON cell and turned-OFF cell are negative (since the sign is inverted, the dotted line and broken line above 0 V represent negative wall voltages). The turned-ON cell is more strongly negatively charged. Negative voltages are gradually applied to the two cells, and the absolute values of the negative cell voltages are increased. Since the turned-ON cell is more strongly negatively charged, the turned-ON cell is discharged at time t1 before the non-turned-ON cell is discharged. At time t1, a waveform representing the discharge (light) in the turned-ON cell rises, as shown in FIG. 4. Once the discharge has started, the wall voltage is accumulated so that the cell voltage is maintained at a discharge starting threshold voltage −Vt1 (positive or negative is indicated by the sign of the discharge starting threshold voltage) having the α electrode as the cathode (hereinafter this is written as “the wall voltage is ‘written’ so that the cell voltage is maintained at the discharge starting threshold voltage). Slightly after the discharge in the turned-ON cell, the turned-OFF cell starts discharging at time t2. At time t2, a waveform representing the discharge (light) in the turned-OFF cell rises, as shown in FIG. 4. Once the discharge has started, the wall voltage of the same value is written so that the cell voltage of the turned-OFF cell is maintained at the discharge starting threshold voltage −Vt1 having the α electrode as the cathode. The wall voltage in this case is represented by the dotted-chain line. Subsequently, when the falling of the negative ramp wave stops (maximum voltage) at time ta, the waveform representing the discharge (light) decreases to level 0. At time t3, the negative ramp wave ends. At this time, the wall voltages of both the turned-ON cell and the turned-OFF cell are set to the same voltage −VR1+Vt1.
The polarity of the applied voltage is inverted. This time, a positive ramp wave is applied. Since the wall voltages of both the turned-ON cell and the turned-OFF cell have been set to the same value at time t3, the two cells simultaneously starts discharging at time t4. Subsequently, the discharges are sustained, and the wall voltages are written while the cell voltages are maintained at a discharge starting threshold voltage Vt2, Waveforms representing the discharges (light) in both the turned-ON cell and the turned-OFF cell rise at time t4 and decrease to level 0 at time tb at which the rising of the positive ramp wave stops. Each of the wall voltages at time t5 at which the positive ramp wave ends is VR2−Vt2.
Since the discharge starting threshold voltage Vt2 is a constant peculiar to a discharge between two electrodes, the wall voltage after the positive ramp wave has ended is determined only by the applied voltage amplitude VR2.
Using the basic principle of the resetting described above, turned-ON cells and turned-OFF cells are reset. In order to describe the principle, the relationship between two electrodes (that is, between α and β electrodes) has been described. Since practical PDP cells each have three types of electrodes consisting of the X electrode, Y electrode, and A electrode, the operation is more complicated.
FIG. 5A shows the resetting waveform portions shown in FIG. 3. Each resetting waveform consists of two steps, namely, a first step and a second step. The potential of the address electrode is fixed to a zero potential during the resetting period. To the X electrode, a negative pulse (constant voltage pulse having an amplitude of −VX1) is applied in the first step and a positive pulse (constant voltage pulse having an amplitude of VX2) is applied in the second step. To the Y electrode, a gradually increasing voltage waveform having an amplitude of VY1 (positive ramp wave) is applied in the first step and a gradually decreasing voltage waveform having an amplitude of −VY2 (negative ramp wave) is applied in the second step.
In order to initiate a discharge between each two electrodes of the three electrodes (X electrode, Y electrode, and A electrode) of the PDP, it is convenient to use two types of “voltages between two electrodes”, that is, between the X and Y electrodes and between the A and Y electrodes, as shown in FIG. 5B. The two types of voltages are voltages between two electrodes on the basis of the Y electrode (that is, the electrode represented by the latter character of a character string representing the two electrodes).
In the first step, a gradually decreasing voltage waveform having an amplitude of −(VX1+VY1) is applied between the X and Y electrodes, and a gradually decreasing voltage waveform having an amplitude of −VY1 is applied between the A and Y electrodes. In the second step, a gradually increasing voltage waveform having an amplitude of VX2+VY2 is applied between the X and Y electrodes, and a gradually increasing voltage waveform having an amplitude of VY2 is applied between the A and Y electrodes.
Referring to FIG. 5B, wall voltages are represented by the dotted lines and plotted while the signs thereof are inverted (the same applies to the following description). There are two types of wall voltages of the PDP having three types of electrodes: a wall voltage between the X and Y electrodes and a wall voltage between the A and Y electrodes.
A cell voltage between the X and Y electrodes is referred to as an XY cell voltage; a voltage applied between the X and Y electrodes is referred to as an XY applied voltage; and a wall voltage between the X and Y electrodes is referred to as an XY wall voltage. Similarly, a cell voltage between the A and Y electrodes is referred to as an AY cell voltage; a voltage applied between the A and Y electrodes is referred to as an AY applied voltage; and a wall voltage between the A and Y electrodes is referred to as an AY wall voltage (the same applies to the following description).
An effective voltage required by each cell's discharge space (cell voltage) is the sum of an applied voltage and a wall voltage:
XY cell voltage=XY applied voltage+XY wall voltage
AY cell voltage=AY applied voltage+AY wall voltage
Since the sign of each of the plotted wall voltages is inverted in FIG. 5B, the cell voltage refers to the distance between the dotted line and the solid line. When the solid line is above the dotted line, the cell voltage is positive. When the solid line is below the dotted line, the cell voltage is negative.
Since the PDP has three types of electrodes, there are discharge starting threshold voltages between the X and Y and between the Y and X electrodes, between the A and Y and between the Y and A electrodes, and between the A and X and between the X and A electrodes. Specifically, there are six types:
VtXY: discharge starting threshold voltage between X and Y electrodes having Y electrode as cathode (hereinafter referred to as an XY discharge starting threshold voltage);
VtYX: discharge starting threshold voltage between Y and X electrodes having X electrode as cathode (hereinafter referred to as a YX discharge starting threshold voltage);
VtAY: discharge starting threshold voltage between A and Y electrodes having Y electrode as cathode (hereinafter referred to as an AY discharge starting threshold voltage);
VtYA: discharge starting threshold voltage between Y and A electrodes having A electrode as cathode (hereinafter referred to as a YA discharge starting threshold voltage);
VtAX: discharge starting threshold voltage between A and X electrodes having X electrode as cathode (hereinafter referred to as an AX discharge starting threshold voltage); and
VtXA: discharge starting threshold voltage between X and A electrodes having A electrode as cathode (hereinafter referred to as an XA discharge starting threshold voltage).
FIG. 6 shows an example of normal resetting. The broken line represents a wall voltage of a cell that has been turned ON in an SF immediately before the start of resetting (hereinafter referred to as a previous SF), and the dotted-chain line represents a wall voltage of a cell that has been turned OFF in the previous SF. In the case of the turned-ON cell, the XY wall voltage immediately before the start of the resetting is negative (please note that the sign is inverted), and the AY wall voltage is zero. In contrast, in the case of the turned-OFF cell, both the XY wall voltage and the AY wall voltage immediately before the start of the resetting are positive (please note that the sign is inverted).
The “turned-ON cell” that has been turned ON in the previous SF will now be described. At time (1), the XY cell voltage exceeds the YX discharge starting threshold voltage −VtYX, and a discharge is initiated in the “turned-ON cell”. Subsequently, the wall voltage is written so that the XY cell voltage is maintained at −VtYX until the amplitude of the XY applied voltage becomes −VxY1 and the amplitude of the AY applied voltage becomes −VAY1. At the same time, the AY wall voltage changes. Since the change in the AY wall voltage is smaller than the change in the AY applied voltage, the absolute value of the AY cell voltage gradually increases. In this example, the AY cell voltage does not exceed the AY discharge starting threshold voltage in the first step, and no discharge is thus initiated. Therefore, the AY cell voltage is not set to a uniform value. At the first step end time (3), only the XY wall voltage is set, whereas the AY wall voltage remains unset.
In the second step, the XY applied voltage and the AY applied voltage increase, and the XY cell voltage and the AY cell voltage increase. At time (4), the XY cell voltage exceeds the XY discharge starting threshold voltage VtXY, and a discharge is initiated. Subsequent to time (4), the XY wall voltage is written so that the XY cell voltage is maintained at VtXY. At the same time, the AY wall voltage is written. Since the change in the AY wall voltage is smaller than the change in the AY applied voltage, the absolute value of the AY cell voltage gradually increases. At time (5), the AY cell voltage exceeds the AY discharge starting threshold voltage VtAY, and a discharge is initiated. The AY wall voltage is written so that the AY cell voltage becomes the constant value VtAY. At the resetting end time (7), both the XY wall voltage and the AY wall voltage are set.
The “turned-OFF cell” that has been turned OFF in the previous SF will now be described. In the first step, at time (2), the XY cell voltage exceeds the XY discharge starting threshold voltage −VtXY, and a discharge is initiated. Subsequently, the XY wall voltage is written so that the XY cell voltage is maintained at −VtYX until the XY applied voltage in the first step becomes −VxY1 and the AY applied voltage becomes −VAY1. At the same time, the AY wall voltage changes. Since the change in the AY wall voltage is smaller than the change in the AY applied voltage, the AY cell voltage gradually increases. In this example, no discharge is initiated since the AY cell voltage does not exceed the AY discharge starting threshold voltage. Thus, the AY cell voltage is not set to the uniform value. At the first step end time (3), only the XY wall voltage is set, whereas the AY wall voltage remains unset.
The operation in the second step will now be described. The XY applied voltage and the AY applied voltage increase, and the XY cell voltage and the AY cell voltage increase. At time (4), the XY cell voltage first exceeds the XY discharge starting threshold voltage VtXY, and a discharge is initiated. Subsequent to time (4), the XY wall voltage is written so that the XY cell voltage is maintained at VtXY. At the same time, the AY wall voltage changes. Since the change in the AY wall voltage is smaller than the AY applied voltage, the AY cell voltage gradually increases. At time (6), the AY cell voltage exceeds the AY discharge starting threshold voltage VtAY, and a discharge is initiated. The AY wall voltage is written so that the AY cell voltage becomes the constant value VtAY. At the second step end time (7), both the XY wall voltage and the AY wall voltage are set.
As described above, in this example, regardless of the ON/OFF state in the previous SF, the XY wall voltages and the AY wall voltages in the cases of the turned-ON cell and the turned-OFF cell are set to the same values, respectively, at the end of the resetting.
What is important in the resetting using the ramp waves is that the cell must be driven so that two simultaneous discharges, that is, a discharge between the X and Y electrodes having the Y electrode as the cathode (hereinafter referred to as an XY discharge) and a discharge between the A and Y electrodes having the Y electrode as the cathode (hereinafter referred to as an AY discharge), are simultaneously initiated immediately before the end of the resetting. On the other hand, the ramp waves in the first step need not initiate two discharges at the same time.
The operation described above is geometrically analyzed using a “cell voltage plane” and a “discharge starting threshold voltage closed curve”, which are presented at an international conference of the Society for Information Display in 2001 (see “High-speed Address Driving Waveform Analysis Using Wall Voltage Transfer Function for Three Terminals and Vt Close Curve in Three-Electrode Surface-Discharge AC-PDPs”, pp. 1022 to 1025, SID 01 DIGEST, 2001).
Referring to FIGS. 7A and 7B, the “cell voltage plane” and “discharge starting threshold voltage closed curve” will now be described. (The contents related to FIGS. 7A and 7B are disclosed in Japanese Unexamined Patent Application Publication No. 2001-242825.)
Since the cell voltages, wall voltages, and applied voltages come in pairs of the X and Y electrodes and the A and Y electrodes, they are represented as two-dimensional voltage vectors, namely, a cell voltage vector (VCXY, VCAY), a wall voltage vector (VWXY, VWAY), and an applied voltage vector (VaXY, VaAY).
A coordinate plane, which is referred to as the “cell voltage plane,” having the XY cell voltage VCXY as the abscissa and the AY cell voltage VCAY as the ordinate is defined. The relationships among the three vectors are visually represented in this plane using points and arrows.
FIG. 7A shows the “cell voltage plane” and the relationship among the three voltage vectors.
Since the discharge starting threshold voltages play an important role in the resetting operation, points of the discharge starting threshold voltages are plotted in the “cell voltage plane”. These points constitute a “discharge starting threshold voltage closed curve” (hereinafter referred to as a “Vt closed curve”).
FIG. 7B shows a measured Vt closed curve. Although the XY discharge starting threshold voltage portion does not constitute a line but constitutes a slightly distorted shape, the “Vt closed curve” has a shape relatively similar to a hexagon. The following description assumes that the “Vt closed curve” has a hexagonal shape. The vertices of the hexagon simultaneously satisfy two discharge starting threshold voltages and play an important role in the resetting operation. Since two discharges are initiated at the six vertices, the six vertices are referred to as “simultaneous discharge points”.
Referring to FIGS. 8A and 8B, a method of determining, from the “cell voltage plane” and “Vt closed curve”, the wall voltage vector that changes in accordance with a discharge upon application of a ramp wave is described.
The wall voltage state prior to application of a ramp wave is at point 0 in FIG. 8A. Upon application of the ramp wave, the cell voltage changes toward point 1 and exceeds the XY discharge starting threshold voltage VtXY. When a discharge is caused by the ramp wave (ramp-caused discharge), once the cell voltage has exceeded the threshold, the wall voltage is written so that the cell voltage is maintained at the threshold. In other words, referring to FIG. 8A, a wall voltage vector 11′ (vector connecting point 1 and point 1′) (and so forth) is written. The discharge is sustained until the absolute value of the ramp wave voltage reaches its maximum. While the XY cell voltage is maintained at around the XY discharge starting threshold voltage VtXY, the AY cell voltage increases. In other words, the cell voltage point changes in a sequence of 1, 1′, 2, 2′, 3, 3′, . . . , 5, 5′ shown in FIG. 8A. A micro-increase in the applied voltage is represented by the solid arrow, and a micro-increase in the wall voltage is represented by the dotted arrow. The micro-increase in the wall voltage will now be described.
Since the XY discharge has been initiated, the charge mainly moves between the X electrode and the Y electrode. When a wall charge of +Q moves to the X electrode and a wall charge of −Q moves to the Y electrode, a wall charge of +Q−(−Q)=2Q moves between the X and Y electrodes, and a wall charge of 0−(−Q)=Q moves between the A and Y electrodes. In the plane having VCXY and VCAY as the coordinate axes, the direction written by the XY discharge has a slope of ½. More accurately speaking, the slope needs to be determined not from the wall charge, but from the wall voltage. The slope depends on the forms and materials of the dielectric layers covering the electrodes of the PDP. The slope is roughly near ½.
The wall voltage vector to be written until the end of the ramp wave is determined as in FIG. 8B. FIG. 8B shows a vector connecting the start point and end point of each applied voltage vector representing the micro-change and a vector connecting the start point and end point of each wall voltage vector representing the micro-change. That is, vector 05 is a total applied voltage vector, and vector 55′ is a total written wall voltage vector.
Point 5 is determined by adding the total applied voltage vector to the initial wall voltage point 0. A line that passes through point 5 and that has a slope of ½ is written. The intersection 5′ of the written line and the “Vt closed curve” is the changed cell voltage point. Vector 55′ is the total written wall voltage. As discussed above, the total wall voltage vector that has been written by the ramp wave and the cell voltage point are determined from the geometric relationship.
In the above description, the cell voltage point is determined from the geometric relationship. The cell voltage is not increased to a very large value, such as point 5 of FIG. 8B. Actually, the cell voltage point moves in the vicinity of the “Vt closed curve”, such as point 5 of FIG. 8A.
The AX discharge and the AY discharge can be analyzed in a similar manner. FIG. 9 shows wall voltage vectors written when the XY discharge, AY discharge, AX discharge, and the like are initiated. Each white dot represents an initial wall voltage. Each solid arrow represents an applied voltage vector. Each dotted arrow represents a wall voltage vector written by a ramp-caused discharge. Each black dot represents a wall voltage point subsequent to the end of the ramp wave. During the XY discharge, a wall voltage vector having a slope of ½ is written. During the AY discharge, a wall voltage vector having a slope of 2 is written. During the AX discharge, a wall voltage vector having a slope of −1 is written. Although these slopes depend on the forms and materials of the dielectric layers covering the electrodes of the PDP, each of the slopes has an approximately equal value.
FIGS. 10A and 10B show the analysis of the operation shown in FIG. 6. Specifically, FIG. 10A shows the operation analysis of the turned-ON cell, and FIG. 10B shows the operation analysis of the turned-OFF cell.
The turned-ON cell in FIG. 10A is at point A prior to resetting. Referring to the waveform shown in FIG. 6, at first the applied voltage changes step-wisely, and the cell voltage point moves to point B. Next, a discharge is initiated at point C upon application of the negative ramp wave, and the writing of the wall voltage starts. Since the discharge is the XY discharge, the writing direction has a slope of ½. The cell voltage is at point E at the end of the first ramp wave. In transition from the first ramp wave to the second ramp wave, the applied voltage suddenly changes, and the cell voltage point moves to point F. Upon application of the second ramp wave, a discharge is initiated at point G, and the writing of the wall voltage starts. Since the discharge is the XY discharge, at first the wall voltage is written with a slope of ½. Subsequent to the start of the discharge, the cell voltage point moves upward along the “Vt closed curve”. This corresponds to the fact that the AY cell voltage increases while the XY cell voltage is maintained at VtXY. As the applied voltage increases, so does the AY cell voltage. When the AY cell voltage becomes the AY discharge starting threshold voltage VtAY, at point I, simultaneous discharges occur between the X and Y electrodes and between the A and Y electrodes (hereinafter the simultaneous discharges are referred to as “XY and AY simultaneous discharges”). After the “XY and AY simultaneous discharges” have occurred, the cell voltage point is fixed at point I. An increase in the applied voltage only causes the wall voltage to be written, and the cell voltage vector remains unchanged.
The turned-OFF cell in FIG. 10B is at point J prior to resetting. Referring to the waveform shown in FIG. 6, at first the applied voltage changes step-wisely, and the cell voltage point moves to point K. Next, a discharge is initiated at point L upon application of the negative ramp wave, and the writing of the wall voltage starts. Since the discharge is the XY discharge, the writing direction has a slope of ½. The cell voltage is at point N at the end of the first ramp wave. In transition from the first ramp wave to the second ramp wave, the applied voltage suddenly changes, and the cell voltage point moves to point O. Upon application of the second ramp wave, a discharge is initiated at point P and the writing of the wall voltage starts. Since the discharge is the XY discharge, at first the wall voltage is written with a slope of ½. Subsequent to the start of the discharge, the cell voltage point moves upward along the “Vt closed curve”. This corresponds to the fact that the AY cell voltage increases while the XY cell voltage is maintained at VtXY. As the applied voltage increases, so does the AY cell voltage. When the AY cell voltage becomes the AY discharge starting threshold voltage VtAY, the “XY and AY simultaneous discharges” occur at point R. Subsequent to the simultaneous discharges, the cell voltage point is fixed at point R. An increase in the applied voltage only causes the wall voltage to be written, and the cell voltage vector remains unchanged.
When the resetting is normally done, the cell voltage point immediately after the end of the resetting is set to the upper-right vertex of the “Vt closed curve” having a hexagonal shape, that is, a point representing the “XY and AY simultaneous discharges”. The point is referred to as a “simultaneous resetting point”. When the cell voltage reaches the “simultaneous resetting point”, the XY wall voltage and the AY wall voltage are simultaneously adjusted to the corresponding values.
Whether the resetting is normally done or not greatly depends on the wall voltage prior to the start of resetting. In other words, even when the same resetting waveform is used, the resetting is normally done or not done depending on the previous wall voltage. The range of the wall voltage in which the resetting is normally done greatly depends on the amplitude of the resetting waveform applied voltage.
FIG. 11 shows a case in which the AY wall voltage prior to the start of resetting differs from that of FIG. 6 whereas the cases shown in FIGS. 6 and 11 have the same driving waveforms. In FIG. 6, the AY wall voltage of the turned-ON cell is zero. In FIG. 11, the AY wall voltage of the turned-ON cell is negative (please note that the sign is inverted).
Only the operation of the turned-ON cell (that is, the behavior of the wall voltage represented by the broken line) will now be discussed.
In the turned-ON cell, the XY wall voltage is written so that the XY cell voltage is maintained at −VtYX during a period from time (1) at which the XY cell voltage exceeds the YX discharge starting threshold voltage −VtYX to time at which the XY applied voltage amplitude becomes −VXY1 and the AY applied voltage becomes −VAY1. At the same time, the AY wall voltage changes. Since the change in the AY wall voltage is smaller than the change in the AY applied voltage, the absolute value of the AY cell voltage gradually increases. In this example, as in FIG. 6, the AY cell voltage does not exceed the AY discharge starting threshold voltage in the first step. Therefore, the AY cell voltage is not adjusted to the corresponding value. At the first step end time (3), only the XY wall voltage is set, whereas the AY wall voltage remains unset.
In the second step, the XY applied voltage and the AY applied voltage increase, and the XY cell voltage and the AY cell voltage increase. At time (4), the XY cell voltage exceeds the XY discharge starting threshold voltage VtXY. Subsequent to time (4), the XY wall voltage is written so that the XY cell voltage is maintained at VtXY. At the same time, the AY wall voltage is written. Since the change in the AY wall voltage is smaller than the change in the AY applied voltage, the absolute value of the AY cell voltage gradually increases. Even by time (5), the AY cell voltage does not exceed the AY discharge starting threshold voltage VtAY and the written AY wall voltage is not sufficient. At the resetting end time (6), the XY wall voltage is set, whereas the AY wall voltage remains unset.
As shown in FIGS. 3 and 5A, the driving waveforms in the resetting period are such that positive and negative driving waveforms, such as those shown in FIGS. 3 and 5A, are applied to the X electrode and the Y electrode, and the address electrode potential is fixed at zero. Therefore, the amplitude of the AY applied voltage is smaller than the amplitude of the XY applied voltage. The range of the wall voltage in which the AY wall voltage is normally reset thus becomes narrower. This results in an increase in the rate of resetting failure of the AY wall voltage. The PDP thus suffers from display problems such as turning ON extra cells or failing to turn ON the cells that must be turned ON.